USING NEW TECHNOLOGIES TO MAP EARTHQUAKE-INDUCED LIQUEFACTION FEATURES IN THE NEW MADRID SEISMIC ZONE

Paleoseismic investigations were conducted in November 2015 just south of the Missouri – Arkansas border and west of the Mississippi River in the small farming community of Yarbro, Arkansas. Within the Mississippi River embayment, fluvial sediments are broadly distributed and susceptible to liquefaction during strong ground shaking, thus providing a record of repeated large earthquakes dating back 4,300 yr B.P. On newly acquired LiDAR imagery, an anomalous lineament was identified north of the Pemiscot Bayou and targeted for field investigations. A DJI Phantom 3 quadcopter was deployed utilizing a 12 Megapixel FC300S camera with a 4000 x 3000 resolution and 3.61 mm focal length that automatically inserts the global positioning satellite information into the exchangeable image file data of each photograph. The pre-programmed flights covered an area of just over 6.5 acres. 85 images were digitally processed using Agisoft Photoscaner and Pix4D to create a point cloud model. The resulting digital elevation data shows a morphological surface that slopes gently toward the west. Other high-resolution data acquisition included the use of a real time kinematic (RTK) Trimble 8 satellite ground station for high precision location of liquefaction features such as dikes as well as subsidence and offset of a paleosol. Trenches excavated across the lineament revealed a paleosol developed on a silty clay deposit. A large sand dike, 177 cm wide, crosscuts the paleosol and is connected to a large sand blow that overlies the paleosol. The paleosol is displaced by 12.5 cm across the dike. The sand dike and paleosol are buried by a compound sand blow composed of three extensive sand layers, suggesting that there were at least three liquefaction events. The lack of soil formation between the layers, further suggests that the three liquefaction events occurred in a relatively short period of time. Although disturbed by plowing, a 25- to 30-cm thick soil has developed in the top of the sand blow suggesting it may be prehistoric in age. Organic samples collected at the site have been submitted for radiocarbon dating but the results are not yet available. Several Woodland sherds found on the ground surface and in the paleosol buried by the sand blow suggest that the liquefaction features may represent a pre-historic earthquake sequence.